A work machine such as a tractor, excavator, front end loader or the like typically includes an internal combustion engine providing motive force to the vehicle as well as providing power for auxiliary components. Auxiliary components may include hydraulic cylinders, hydraulic brakes, hydraulic fan motors, or other fluid actuated devices.
It is known to utilize an independent metering valve (IMV) assembly in association with an internal combustion engine. Such an independent metering valve assembly typically receives pressurized hydraulic fluid from a hydraulic pump and is in fluid communication with a single hydraulic load providing a single hydraulic function. For example, an IMV assembly may be fluidly coupled with a two-way hydraulic cylinder used for a single output function (e.g., tipping a loader bucket on a front end loader). The IMV assembly typically includes four independently controllable valves, with one pair of the valves being coupled with the head end of the hydraulic cylinder and the other pair of controllable valves being coupled with the rod end to the cylinder. Each pair of controllable valves in the IMV assembly allows flow both to and from the hydraulic cylinder. The controllable valves are electronically controlled using a controller, depending upon various input signals received from one or more sensors. An example of an IMV assembly utilized for a single hydraulic function is disclosed in U.S. Pat. No. 5,960,695 (Aardema et al.), which is assigned to the assignee of the present invention.
An auxiliary component in the form of a hydraulic fan motor as described above is used for cooling the internal combustion engine. However, cooling requirements for internal combustion engines are subject to wide variations depending upon operating conditions. When the engine is cold, little or no cooling is required. During engine operation, the necessary cooling typically varies as a function of engine load, and with external conditions such as air temperature and wind or vehicle velocity. Driving a hydraulic fan motor in a continuous manner may thus not be desirable both from a parasitic power consumption stand point as well as operating efficiency of the engine.
The present invention is directed to overcoming one or more of the problems as set forth above.